Re: [PATCH net-next 4/4] ethtool: runtime-resume netdev parent in ethnl_ops_begin

[Julian Wiedmann <jwi@linux.ibm.com>]

On 01.08.21 13:41, Heiner Kallweit wrote:
> If a network device is runtime-suspended then:
> - network device may be flagged as detached and all ethtool ops (even if not
>   accessing the device) will fail because netif_device_present() returns
>   false
> - ethtool ops may fail because device is not accessible (e.g. because being
>   in D3 in case of a PCI device)
> 
> It may not be desirable that userspace can't use even simple ethtool ops
> that not access the device if interface or link is down. To be more friendly
> to userspace let's ensure that device is runtime-resumed when executing the
> respective ethtool op in kernel.
> 
> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
> ---
>  net/ethtool/netlink.c | 31 +++++++++++++++++++++++++------
>  1 file changed, 25 insertions(+), 6 deletions(-)
> 

[...]

>  
>  void ethnl_ops_complete(struct net_device *dev)
>  {
>  	if (dev && dev->ethtool_ops->complete)
>  		dev->ethtool_ops->complete(dev);
> +
> +	if (dev->dev.parent)
> +		pm_runtime_put(dev->dev.parent);
>  }
>  
>  /**
> 

Hello Heiner,

Coverity complains that we checked dev != NULL earlier but now
unconditionally dereference it:


*** CID 1506213:  Null pointer dereferences  (FORWARD_NULL)
/net/ethtool/netlink.c: 67 in ethnl_ops_complete()
61     
62     void ethnl_ops_complete(struct net_device *dev)
63     {
64     	if (dev && dev->ethtool_ops->complete)
65     		dev->ethtool_ops->complete(dev);
66     
>>>     CID 1506213:  Null pointer dereferences  (FORWARD_NULL)
>>>     Dereferencing null pointer "dev".
67     	if (dev->dev.parent)
68     		pm_runtime_put(dev->dev.parent);
69     }
70     
71     /**
72      * ethnl_parse_header_dev_get() - parse request header